The activity of the biotinyl enzyme, acetyl-CoA carboxylase, is reduced in biotin-deficient chicks. Administration of inorganic mercury salts to biotin-deficient chicks stimulates fatty acid synthesis. Since acetyl-CoA carboxylase is the rate-limiting enzyme for fatty acid synthesis, the above-mentioned effect of mercury is presumably a result of interaction with this enzyme. Mercury does not appear to affect tissue levels of citrate which is an effector of acetyl-CoA carboxylase. Therefore, our working hypothesis for the coming year is that mercury increases tissue levels of acetyl-CoA carboxylase. To test this hypothesis, enzyme from chicken liver will be purified to homogeneity and injected into rabbits. Anti-carboxylase antibodies will be isolated from rabbit serum and used to quantitate enzyme in extracts from livers of biotin-deficient chicks, both with and without prior treatment with mercury. The results should answer the question of whether or not the increased lipogenic activity of biotin-deficient chicks treated with mercury is the result of synthesis of more acetyl-CoA carboxylase or stimulation of the activity of pre-existing enzyme.